Thanks for a great description!
A couple of questions:
A bulkhead fitting should have a rubber gasket that will seal properly without additional sealant
Since bulkhead fittings were suggested, I've been looking them up. The installation seems easy enough, but in all the videos I see I am stuck with a hole with threads on the outside, no one shows what comes next. What are the parts I would need for this? Do I need a join to connect the threads on the outside of each container?
The sides of the container won’t be parallel to the ground, so a straight pipe will put strain on the container that will lead to a failure. You will probably want to use flexible hose to connect the two containers, but two 45 degree elbows at each end of ridgid pipe(so 4 total) can take the strain out once you play with the orientations.
I didn't really understand this. Do you mean there will be strain due to the downward force exerted by the weight of the pipe and water? I'm hoping to have the distance between the tanks as short as possible, and the diameter should also not be too big.
I've been using a Merkur Progress for ten years now. The adjustability of the action makes it more versatile, which makes it easier to adjust to different types of blades. I use Astra Superior blades, but also have a stack of Shark blades that I at some point liked, and some Feather blades that are insanely sharp and unforgiving.
Make sure you learn how to lather properly. A good lather makes all the difference, and it also a major factor in making it a lot more enjoyable than the canned Gillette-stuff. I use Proraso for my run-of-the-mill shaves, and have over the years bought a variety of hard soaps as well. My favorite is Marlborough from D.R. Harris.
EDIT: I had one of those starter razors from Mühle in the beginning (Rytmo?). It snapped in two at the neck after I dropped it by accident, after 6 months use. I still have the synthetic hair brush that came with it. Some people go really into brushes, but I've been happy with mine.